Rendering haml partials takes a long time... why?

Question

My Rails 3.0 app on ruby 1.8.7 contains Haml 3.1.3. Most of the views are haml templates, it takes about 0.5-5ms to render them on my machine in production mode.

Having said that, a few partials take much longer. 300ms to 900ms for 30-60 lines of haml. It must be something in the way how I use it, but how could I debug what's wrong? The benchmarks are consistent and reproducible.

I'm not sure about possible sources of the error:

deep partial nesting? (3-5 levels)
deep haml nesting? (4-8 levels)
use of block helpers?
lots of translations?
using haml with formtastic 2.0?
using form builders for nested forms?

Any help is appreciated.

Currently I'm looking into Formtastic 2.0.2 as a source for this problem. Ive filed a bug report on github: https://github.com/justinfrench/formtastic/issues/744 — datenimperator, Nov 17 '11 at 16:31
You haven't answered my question. And why do you think Formtastic is responsible? — Marnen Laibow-Koser, Nov 17 '11 at 16:32
I've found (through ruby-prof) `image_tag` and `form_for` take a lot of time, and replacing them with HTML and `#{interpolation}` is much faster. — Chloe, Mar 08 '14 at 06:14

score 1 · Accepted Answer · edited May 23 '17 at 12:17

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It turned out to be a number of things inside Formtastic 2.0:

Lots of object lookups, uncached
Lots of translations, uncached
Use of try…rescue blocks which slowed it down tremendously

Fixes have been added to Formtastic 2.1 and up, making it a lot faster. Kudos to Sascha Konietzke for providing patches.

edited May 23 '17 at 12:17

Community

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answered Nov 28 '12 at 09:05

datenimperator

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score 1 · Answer 2 · answered Aug 11 '16 at 10:35

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A more recent way to fix this is Hamlit, a high-performance Haml implementation with some limitations by design for performance. It claims 8.24x speedup.

Also, not Haml-specific, but look at multi-fetch gem for lists.

answered Aug 11 '16 at 10:35

mahemoff

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Thanks for mentioning hamlit, which indeed is faster. In this particular case uncached translations have been causing this, but adding a little extra speed is nice nonetheless. – datenimperator Aug 12 '16 at 14:56
Interesting, I haven't heard of that before. Any info on how to make sure translations are being cached correctly? (I'm always up for anything to improve Rails rendering perf!) – mahemoff Aug 13 '16 at 18:17

score 0 · Answer 3 · answered Jun 11 '12 at 20:26

Most likely it's Garbage Collection. See these posts:

http://www.williambharding.com/blog/uncategorized/rails-3-performance-abysmal-to-good-to-great/comment-page-1/

http://bibwild.wordpress.com/2011/06/28/rails3-unbearably-slow-view-rendering-use-ree-with-gc-tuning/

If you're using REE 1.8.7 (which also fixes a memory leak, so you should be) then you can tune your GC settings. I just did this last week and our response time dropped by 50%.

score 0 · Answer 4 · answered Feb 19 '15 at 13:50

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Put in .bashrc:

export RUBY_GC_HEAP_INIT_SLOTS=1000000
export RUBY_HEAP_SLOTS_INCREMENT=500000
export RUBY_HEAP_SLOTS_GROWTH_FACTOR=1
export RUBY_GC_MALLOC_LIMIT=50000000

Source, and restart server

$> source ~/.bashrc
$> rails s

Depending on what is your problem, this might make rendering your partials faster (in my case, average rendering time got x3 faster).

answered Feb 19 '15 at 13:50

Benjamin Crouzier

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What OS/machine and Ruby runtime did you use these settings on? – mahemoff Aug 04 '16 at 21:39
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@mahemoff this was a while ago, but I think a 2013-macbook pro with 16gb ram – Benjamin Crouzier Aug 05 '16 at 15:23
Lol exactly same rig here :) Thanks. – mahemoff Aug 05 '16 at 19:47

Rendering haml partials takes a long time... why?

4 Answers4